Variable gas turbine engine air intake

ABSTRACT

A vortex air flow is set up around the outer fringe of an air flow through a duct, the internal diameter of which increases in a downstream direction. The vortex picks up the outer fringe of the air flow in the duct and causes it to diffuse more rapidly onto the increased diameter portion of the duct, than would normally occur.

' United States Patent Poucher et al.

[ 51 MayZ, 1972 [54] VARIABLE GAS TURBINE ENGINE AIR INTAKE [72]Inventors: Michael Poucher, Duffield; Michael Roy Willlams, Filton, bothof England I 73] Asaignee: Rolls-Royce Limited, Derby, England [221Filed: July 13, 1970 [21] Appl. No.: 54,124

[30] Foreign Application Priority Data July 30, 1969 Great Britain..38,l50/69 [52] US. Cl. ..60/39.29, 60/269, l37/lS.1, 138/39, 415/D1G.1 [51] Int. Cl. ..F02c 7/04 [58] Field of Search ..60/39.29, 269;137/13, 15.1, 137/815; 138/39; 4l5/DIG. 1

[56] References Cited UNITED STATES PATENTS 2,841,182 7/1958 Scala..60/39.65

2,957,306 10/1960 Attinello ..415/D1G. 1 3,000,401 9/1961 Ringleb......l38/39 3,123,285 3/1964 Lee ..137/81.5 3,285,501 11/1966 McDonald......415/D1G. 1 3,300,121 1/1967 Johnson ...415/D1G. 1 3,430,640 3/1969Lennard ..137/l 5.1 3,508,561 4/1970 Cornish 1 37/8 1 .5 3,524,4588/1970 Goldsmith ..l37/15.1

Primary Examiner-Douglas Hart Attorney-Cushman, Darby & Cushman ABSTRACTA vortex air flow is set up around the outer fringe of an air flowthrough a duct, the internal diameter of which increases in a downstreamdirection. The vortex picks up the outer fringe of the air flow in theduct and causes it to difiuse more rapidly onto the increased diameterportion of the duct, than would normally occur. I

7 Claims, 4 Drawing Figures P'A'TENTEDMAY 2 m2 3,659,418

SHEET 2 OF 3 f:,\(5\f 34 72 5a 74 O Inventors MJAWEL F aua/5e Mos 454 wlZ/Z 4/4/ 4:

M L MM The present invention relates to diffusing ducts for fluid flowsand has particular reference to diffusers in which the fluid flow isstabilized by means of vortices.

According to the invention a diffusing fluid flow duct comprises anupstream wall portion and a downstream wall portion with a discontinuitytherebetween, means adjacent the discontinuity for promoting theformation of a vortex which forms a moving fluid wallbetween said wallportions and which circulates in a direction such as to promoteattachment of a fluid flow leaving the upstream wall portion onto thedownstream wall portion.

The vortex may be an artificially generated forced vortex or may be afreely generated vortex.

In one embodiment of the invention the diffusing duct forms a part of anair intake duct of a gas turbine engine and the discontinuity is formedby at least one flap member which may be moved radially of the duct axisto decrease the flow area of the intake.

In a second embodiment of the invention the diffusing duct is formedbetween the final compressor stage and the combustion chamber of a gasturbine engine. In this embodiment the discontinuity occurs between theupstream portion of the diffusing duct which receives air from the laststage of the compressor, and the casing surrounding the combustionchamber.

The means promoting the formation of a vortex comprises at least oneannular, downstream-facing concave member extending across thediscontinuity and into which part of the expanding fluid flow will breakaway to form a vortex. Preferably one concave member is provided on eachside of the diffuser extending respectively from the upstream portion ofthe diffuser to the radially outer and inner casings of the combustionchamber respectively.

The invention will now be more particularly described, merely by way ofexample with reference to the accompanying drawings in which:

FIG. 1 is a diagrammatic elevation of a gas turbine engine in which theinvention has been incorporated. FIGS. 2 and 3 are enlarged views of onehalf of the intake of the engine of FIG. 1 showing the invention appliedto the intake.

FIG. 4 is an enlarged view of a diffusing duct incorporating theinvention between the compressor and combustion chamber of the engine.

In FIG. 1 a gas turbine engine of the ducted fan type is indicatedgenerally by the numeral 10. The engine comprises, in flow series, anair intake 11, a fan stage 12 surrounded by a cowl 14, a compressor 16,combustion equipment 18, an expansion turbine (not shown) and an exhaustduct which terminates in a hot gas exhaust nozzle 22.

Cowl 14 also terminates in an exhaust nozzle 24, which nozzle exhaustsfan air.

As can be seen in FIG. 1, fan blades 12 extend radially beyond a casing26 which encloses the hot gas producing portion of engine 10, into aduct 28 formed between cowl l4 and engine casing 26. Cowl l4 and enginecasing 26 are maintained in spaced-apartrelationship by a plurality offixed struts 30 equi-angularly spaced about the engine axis.

It is well known in the art that when fan 12 is rotated, ambient air issucked through air intake 11 and forced by fan 12 through duct 28, to befinally expelled from nozzle 24. Passage of the air between the bladesof fan 12 results in wakes being formed in the airflow, said wakesstarting at the trailing edges of the fan blades. The wakes extenddownstream and collide with the leading edges of the struts therebycreating noise pulses which rebound from the strut leading edges andpass upstream, back through the fan blades and out of intake 11.

In order to reduce the volume of noise issuing from the intake 11, theupstream end of the intake is constructed so as to permit variation ofthe cross-sectional area of the intake throat by way of reductionthereof and so increase the velocity of the airflow through the throat.Thus as seen in FIGS. 2 and 3, the fan cowl 14 comprises a double walledstructure, the

inner wall 32 of which comprises, at its upstream end, a plurality ofpairs of flaps 34 and 36, each pair being aligned axially of the engine.

Flaps 34 are each suspended at two points 38 and 40 respectively, whichpoints are pivotally connected to the ends of a pair of links 42 and 44.The other end of link 44 is pivotally attached to-the inside of cowl 14at 46 and the other end of link 42 is pivotally attached to an axiallymoveable member 48. Member'48 achieves its axial movement via the actionof a ram mechanism 50 fixed to cowl l4.

Flaps 36 each have a simple pivot connection 52 to the inside of cowl14. However, flaps 34 and 36 are connected to each other by a pin andslot arrangement 54. Thus when rotation of the intake throatcross-sectional area is required, ram 50 is caused to extend and, in sodoing, pushes link .42 in an upstream direction. Link 42 is pivotallyconnected at 56 to link 44 and so causes link 44 to pivot about the axisof joint 46 and so moves flap 34 from the position shown in FIG. 2, tothe position shown in FIG. 3. The slot and pin connection 54 allows flap34 to move and, at the same time, causes flaps 36 to pivot about theaxis of joint 52 so that, on completion of flap movement to the throatarea reduction position of FIG. 3, there is, at most, a small break inthe intake wall. This break is indicated by the numeral 58.

A problem which is created by throat area reduction in this manner, isthat the design diffusion angle of the intake wall is increased. Thediffusion angle is that angle to the engine axis at which the airspreads out on its way to the fan or compressor face, after passing thethroat plane and, in FIG. 2 is represented'by the Greek letter 0. Thearrows 60 in FIG. 3 indicate the fringe of the main intake airflow afterpassing the reduced throat, the fringe being well away from the intakewall due to movement of the flaps with consequent separation.

As can be seen in FIG. 3 an area of low pressure 62 is thus formed andthe intake air tends to break away at its fringes and fill this areawith a turbulent flow which extends right to the fan or compressor face,further aggravating noise and vibrational problems and resulting in anoverall pressure loss through the engine.

In order to maintain the airflow adjacent the intake wall while flaps 34and 36 are in their operative positions, the adjacent ends of said flapsare formed so that they form between them a substantially toroidalshaped cavity 64, one part of which is in communication with the airintake 11. An air tapping is taken from a position downstream ofcompressor 16 and led, via a conduit 66 to a pair of nozzles 68 and 70in each of flaps 36. Nozzle 68 directs some of the tapped air around thewall of the toroid and off the lip 72 of flap 34. Thus a vortex isformed by the tapped air swirling around in space 64. As the air swirlsofi' lip 72 it merges with and picks up the fringe of the main intakeairflow, causing it to diffuse at a much steeper angle to the engineaxis than angle 0 and thus causes the intake air to contact the intakewall at a position well upstream of the fan or compressor, as indicatedby arrow 74. The early contact of the air with the intake wall obviatesbreakaway and turbulence thereof and so, in turn, does not aggravate theexisting noise and vibration problems mentioned heretofor.

Nozzles 70 direct the remainder of the tapped air onto the intake wall,in a downstream direction, so as to provide in effect, a moving wall forthe intake air to pass along towards the fan, thus reducing thescrubbing action of the air against the static wall, which reductionassists in maintaining the intake air velocity right up to the fan.

Referring now to FIG. 4 there is shown the diffusing diffusing sectionof the gas turbine engine between the last stage of the compressor andthe combustion chamber 101.

The diffusing duct is annular and comprises an upstream portion 102 anddownstream portions 103 with discontinuities 104 therebetween.

The upstream portion 102 comprises a single annular member 105 which issupported from the engine outer casing 106 by a support structure 107.The downstream portion 103 which comprises two annular portions, isformed between the upstream end of the combustion chamber 101 and theradially outer and radially inner casings 106 and 108.

Fluid flow passing down the upstream portion 102 would tend to-break upat the discontinuity and produce turbulence. The discontinuity istherefore bridged by a downstream facing concave annular wall 110 whichis shaped to pick up the breaking flow and guide part of it into avortex flow pattern in the discontinuity. The vortex then acts as afluid wall the shape of which varies with the varying flow velocities ofdifferent engine running conditions and promotes a more stable fluidflow across the discontinuity.

This arrangement is preferable to inserting a shaped wall for guidingthe fluid flow across the discontinuity because the wall would be thecorrect shape only for one particular running condition of the engine.The vortex size and shape however varies with the pressures andvelocities of the fluid under different conditions and maintains a fluidwall of more nearly the correct shape under off-design conditions'andreduces pressure losses in the flow.

We claim:

1. A gas turbine engine comprising: an air intake, compressor means,combustion equipment and turbine means in flow series, said air intakehaving at least one diffusing fluid flow duct for flow of fluidtherethrough and said duct comprising an upstream wall portion and'adownstream diverging wall portion adapted to be spaced therefrom todefine a discontinuity therebetween, said upstream wall portion anddownstream diverging wall portion being formed by pairs of flap members,each pair of said flap members being adjacent axially of the duct witheach other and hinged so as to be moveable to reduce said ducts widthrelative to its width downstream of the upstream wall portion anddownstream diverging wall portion, means defining a toroidal cavitybetween said upstream wall portion and said downstream diverging wallportion, said toroidal cavity being adapted to be open to saiddiscontinuity between said upstream wall portion and said downstreamdiverging wall portion, and means for promoting a fluid vortex in saidtoroidal cavity to define a variable shaped fluid wall across saiddiscontinuity, said fluid vortex circulating in a direction to impingeupon and promote attachment of fluid flowing in said duct leaving theupstream wall portion onto the downstream wall portion without breakawayand turbulence along said downstream diverging wall portion.

2. A gas turbine, engine as claimed in claim 1 wherein adjacent edges ofeach pair of flap members include structure defining a portion of saidtoroidal cavity when said flap members are moved to a position reducingwidth of said duct.

3. A gas turbine engine as claimed in claim 2 wherein the fluid flowingin said air intake has an angle of difiusion of its outer layers whichis increased by impingement thereon of fluid from said fluid vortex whensaid flap members are moved to said width reducing position.

4. A gas turbine engine as claimed in claim 2 wherein said means forpromoting the fluid vortex in said toroidal cavity includes an airtapping conduit extending from a source of compressed air and opening atleast to said toroidal cavity.

5. A gas turbine engine as claimed in claim 4 including nozzle meansalso connected to said tapping conduit for directing some of the airalong the downstream diverging wall portion to provide a moving wallthere along.

6. A gas turbine engine as claimed in claim 2 including means to providea moving fluid wall along said diverging downstream wall portion betweenthe same and outer layers of the fluid flowing in said duct.

7. A gas turbine engine as claimed in claim 6 in which said lastmentioned means includes nozzle means operatively connected to a sourceof compressed air.

* i t t t

1. A gas turbine engine comprising: an air intake, compressor means, combustion equipment and turbine means in flow series, said air intake having at least one diffusing fluid flow duct for flow of fluid therethrough and said duct comprising an upstream wall portion and a downstream diverging wall portion adapted to be spaced therefrom to define a discontinuity therebetween, said upstream wall portion and downstream diverging wall portion being formed by pairs of flap members, each pair of said flap members being adjacent axially of the duct with each other and hinged so as to be moveable to reduce said ducts width relative to its width downstream of the upstream wall portion and downstream diverging wall portion, means defining a toroidal cavity between said upstream wall portion and said downstream diverging wall portion, said toroidal cavity being adapted to be open to said discontinuity between said upstream wall portion and said downstream diverging wall portion, and means for promoting a fluid vortex in said toroidal cavity to define a variable shaped fluid wall across said discontinuity, said fluid vortex circulating in a direction to impinge upon and promote attachment of fluid flowing in said duct leaving the upstream wall portion onto the downstream wall portion without breakaway and turbulence along said downstream diverging wall portion.
 2. A gas turbine engine as claimed in claim 1 wherein adjacent edges of each pair of flap members include sTructure defining a portion of said toroidal cavity when said flap members are moved to a position reducing width of said duct.
 3. A gas turbine engine as claimed in claim 2 wherein the fluid flowing in said air intake has an angle of diffusion of its outer layers which is increased by impingement thereon of fluid from said fluid vortex when said flap members are moved to said width reducing position.
 4. A gas turbine engine as claimed in claim 2 wherein said means for promoting the fluid vortex in said toroidal cavity includes an air tapping conduit extending from a source of compressed air and opening at least to said toroidal cavity.
 5. A gas turbine engine as claimed in claim 4 including nozzle means also connected to said tapping conduit for directing some of the air along the downstream diverging wall portion to provide a moving wall there along.
 6. A gas turbine engine as claimed in claim 2 including means to provide a moving fluid wall along said diverging downstream wall portion between the same and outer layers of the fluid flowing in said duct.
 7. A gas turbine engine as claimed in claim 6 in which said last mentioned means includes nozzle means operatively connected to a source of compressed air. 